The present disclosure relates generally to aircraft safety, and, more particularly, to aircraft fuel tank inerting. Specifically, the present disclosure concerns membrane-based air separation modules (ASMs).
As an aircraft consumes fuel during flight, atmospheric air consisting largely of nitrogen and oxygen enters its fuel tanks. The presence of atmospheric air in the fuel tanks increases the risk of combustion as oxygen mixes with fuel vapors. In order to prevent combustion, the void left by fuel consumption is filled with an inert gas, such as nitrogen. A nitrogen generation system (NGS) includes an ASM, which produces nitrogen-enriched air (NEA) for inerting the fuel tanks. Ideally, the concentration of oxygen in the fuel tanks is less than twelve percent. The presence of NEA substantially reduces the risk of combustion.
A membrane-based ASM includes a polymeric membrane for separating atmospheric air into NEA and oxygen-enriched air (OEA). Polyimide is commonly used to form the tubular membranes within a membrane-based ASM canister. Polyimide is advantageous, in large part, due to its ozone resistance while the aircraft is in flight. However, polyimide is particularly susceptible to damage from exposure to nitrogen oxide (NOx) and sulfur oxide (SOx) from engine exhaust during ground operations. In the presence of water, these acidic gases cause deterioration, necessitating membrane replacement.